1. Field of the Invention
This invention relates generally to the field of human physiology, and, more particularly, to methods, apparatus, systems, software and computer program products for coordinating musculoskeletal and cardiovascular hemodynamics during rhythmic physical activity.
2. Related Art
Blood is circulated through the body by the heart during its pumping cycle, which consists of two distinct periods systole and diastole. Heart muscle (myocardium) contracts to eject blood from the ventricles during the systolic period of each cardiac cycle. This ejection of blood generates arterial blood pressure and flow adequate to deliver blood to tissues throughout the body, thereby transporting oxygen, nutrients and metabolic products, removing carbon dioxide and waste, and facilitating critical physiological functions such as heat exchange. Unlike the rest of the body, which receives most of its arterial blood flow as a result of pressure generated during systole, the heart's own arterial blood supply is delivered primarily during the diastolic portion of the cycle when the heart muscle is relaxing and the heart chambers are filling with venous blood for the next contraction. During this diastolic period, residual blood pressure in the aorta drives blood flow through the coronary arteries and into the myocardial muscle, supplying the heart with its needed oxygen and nutrients.
During physical activity, the musculoskeletal (MSK) system also plays an important role in circulating blood throughout the body. During rhythmic physical activities, two factors commonly cause regular oscillations in peripheral arterial and venous blood pressure and flow: skeletal muscle contraction and relaxation cycles that intermittently compress arterial and venous vasculature, and inertial changes from physical movements that redistribute the person's intravascular blood volume.
When skeletal muscle contractions or MSK movements are favorably coordinated with the heart's pump cycle, the two pumping systems can augment one another, thereby increasing blood flow and perfusion to, through, and from important areas of the body, with less pumping energy expended by the heart. This favorable coordination of the two pumping systems can be referred to as “musculoskeletal counterpulsation” (MCP). During periods of sustained MCP, maximum rhythmic MSK-induced blood pumping consistently increases blood flow into the central circulation while the heart is relaxing and refilling between contractions, and maximum cardiac-induced pumping consistently increases blood flow during maximal MSK relaxation. On the other hand, when rhythmic muscle contractions and MSK movements occur with uncoordinated, or worse, unfavorably coordinated timing, the efficiency and effectiveness of blood pumping is decreased. Unfavorable coordination occurs, for example, when the cardiac pump cycle (CC) and MSK activity cycle (MSKC) consistently pump blood—from opposing directions—maximally into the central circulation at substantially the same time during rhythmic physical activity. This unfavorable coordination of the two pumping systems can be referred to as “inverse musculoskeletal counterpulsation” (iMCP).
Typically, when individuals walk, run, bicycle, or participate in any rhythmic physical activity, most experience only intermittent favorable coordination between MSKC blood pumping and CC blood pumping. Even when an individual's heart rate (HR) and exercise cadence happen to be equal, the respective timing of the two pumps may be favorably coordinated, unfavorably coordinated, or somewhere in between. Research has shown that a certain degree of “cardio-locomotor synchronization” can naturally occur during rhythmic physical activity. However, when such synchrony does occur, it is usually only a temporary phenomenon.
The benefits of a favorable coordination between an individual's MSKC and their CC timing can include improved perfusion and oxygenation of cardiac and peripheral skeletal muscle and possibly other tissues; increased cardiac preload and stroke volume; a lower heart rate (HR); a decrease in systolic blood pressure and pulse pressure; a decrease in required respiratory effort; and less muscle fatigue due to improved skeletal muscle perfusion. All of these benefits can combine to result in physiological advantages that may include decreased myocardial stress, increased aerobic energy production capabilities, improved potential for aerobic fat metabolism, preservation of muscle glycogen stores, enhanced individual performance, and a potential increase in the health benefits and safety of rhythmic physical activity. Conversely, lack of coordination or unfavorable coordination between MSKC and the heart's pump cycle can drive physiology in the opposite direction.
Prior U.S. patent application Ser. No. 13/589,073 (pub. No. US 2013/0171599) and Ser. No. 14/216,960, both assigned to Pulson, Inc., the assignee of the present disclosure, describe several systems and methods that can enable a user to favorably coordinate their MSKC and CC timing. One of the general approaches described in these prior applications provides adaptive real-time biofeedback prompts to a user while engaged in a repetitive physical activity, requiring the user to voluntarily and consistently coordinate their activity timing according to the provided prompts. While most users are able to easily utilize this approach, some might find the prompts difficult to follow or have difficulty maintaining the needed focus in the presence of distractions. In addition, some users may prefer a more automatic approach that requires less of their attention. Accordingly, there is a need to enable MCP during rhythmic physical activities by means that do not require the persistent attention of the user.